I think they should go for somewhere between the Capullomobile and a Tron futuristic/sleek look.

Try to picture a Tron bike (with less light) but in Batmobile form. That's what's in my head. (Accompanied by a Trent Reznor electronic score and shot by Rian Johnson or Fincher to go along with this overall look

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I also think it should be extremely quiet; or at least only make a low ominous noise; it's electric, not a loud engine.

I like some aspect's of the examples in previous posts, but overall they're too 'car'-like. Like Batman just souped up a real car and has to take it to the gas station and stuff.